Earlier this year, consumer group Which? called for mandatory traffic light labelling post-Brexit, warning that inconsistent information on popular adult breakfast cereals could be misleading shoppers about how much sugar, salt and fat they contain.

Its researchers analysed 31 cereals, porridges and granolas and found they could contain more than three quarters of an adult's recommended daily maximum of free sugars in one portion - with the true sugar level not reflected on the packaging.

Sue Davies, Which? strategic policy adviser, said: "While this is a very positive move from Kellogg's, it should apply to all the brand's products sold in the UK and Ireland, not just 80% of them.

"The Government should now use Brexit as an opportunity to introduce legislation that makes traffic light labelling mandatory as part of an approach based on high food standards and aimed at boosting the nation's health and well-being."